Inhibition of phosphoprotein phosphatases blocks metabotropic glutamate receptor effects in the rat nucleus tractus solitarii

Steven R. Glaum*, Richard J. Miller

*Corresponding author for this work

Research output: Contribution to journalArticle

24 Scopus citations

Abstract

Whole-cell recordings were made from dorsomedial nucleus tractus solitarii neurons in thin coronal medullary slices of the rat, at the level of the area postrema. Monosynaptic excitatory postsynaptic currents (EPSCs) were evoked in the tractus solitarius by electrical stimulation in the presence of D-2- amino-5-phosphonopentanoic acid (AP5) and bicuculline. Currents were also evoked by pressure ejection of (S)-α-amino-3-hydroxy-5-methylisoxazole-4- propionate (AMPA) in the presence of AP5, bicuculline, and tetrodotoxin or muscimol in the presence of 6,7-dinitroquinoxaline-2,3-dione and AP5. The metabotropic glutamate receptor (mGluR) agonist (1S,3R)-1-aminocyclopentane- 1,3-dicarboxylate [(1S,3R)-ACPD] reversibly depressed the EPSC and muscimol currents and reversibly potentiated AMPA currents. The effects of (1S,3R)- ACPD were blocked in the presence of a low concentration of the phosphoprotein phosphatase (PP)1 and PP2A inhibitor okadaic acid (OA) but not by a low concentration of the PP inhibitor calyculin A. The immunosuppressant agent FK506 failed to block (1S,3R)-ACPD effects on AMPA currents. However, (1S,3R)-ACPD applied in the presence of FK506 produced a reversible potentiation of muscimol currents. We previously demonstrated that the cell- permeant cGMP analog 8-Br-cGMP can mimic many of the effects of (1S,3R)- ACPD. OA antagonized the effects of 8-Br-cGMP in the present investigation. Finally, we previously demonstrated that brief tetanic stimulation results in the activation of a presynaptic mGluR autoreceptor and depression of subsequently evoked EPSCs. OA similarly blocked tetanus-induced depression of EPSCs. These findings suggest that mGluRs on tractus solitarius afferents and first-order nucleus tractus solitarii neurons may modulate glutamate release and AMPA and γ-aminobutyric acid type A receptor activity via activation of one or more PPs, such as PP2A and/or calcineurin.

Original languageEnglish (US)
Pages (from-to)1221-1226
Number of pages6
JournalMolecular pharmacology
Volume45
Issue number6
StatePublished - Jun 1994

ASJC Scopus subject areas

  • Molecular Medicine
  • Pharmacology

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